Turbo-generator with gas cooling in closed cycle



May 19, 1959 E. WIEDEMANN TURBQGENERATOR WITH GAS COOLING IN CLOSEDCYCLE Filed Sept. 13, 1956 INVENT OR a WM BY ,JQWJ/ZAM United StatesPatent -TURBO-GENERATOR WITH GAS COOLING IN 'CLOSED CYCLE EiigenWiedemann, Hasel, Spreitenbach, Switzerland, as-

signor to Aktiengesellschaft Brown, Boveri & Cle, Baden, Switzerland, ajoint-stock company Application September 13, 1956, Serial No. 609,693

Claims priority, application Germany September 21, 1955 Claims. (Cl.310-58) This invention relates to gas-cooled turbo-generators.

Turbo-generators with gas cooling in closed cycle conventionally areprovided with gas currents for the cooling of the rotor and of thestator, which gas currents are forced at various speeds through theturbo-generator in order to provide for a higher velocity of flow of thecooling gas for the cooling of the rotor than that required for thestator. There are also known installations wherein both of these gascurrents are produced by a common ventilator or compressor, mounted onthe generator shaft; as well as those wherein, for production of bothgas currents, there are provided one or more special ventilators on thegenerator shaft.

In all of these installations it is, in general, necessary to usemultiple-stage fans or compressors for production of high velocity ofcooling gas flow. These installations are attended with the disadvantagethat they enlarge the total length of the apparatus, particularly ifhydrogen is used as cooling gas, since due to its slight specific weighta comparatively large number of compressor stages is required to achievean adequate pressure.

According to the present invention, this disadvantage is eliminated inthat in turbo-generators with gas cooling in closed cycle and separategas circulating devices for the stator and rotor cooling, there isprovided a gas circulating apparatus for the cooling gas flow throughthe rotor, disposed outside of the turbo-generator. For re-cooling ofthe gas flow actuated by the gas circulating apparatus there is provideda special cooler which is, suitably, disposed outside of theturbo-generator. In the latter installation, the coolers provided inknown way inside the turbo-generator can be dimensioned comparativelysmall since, in principle, they should need to lead away only the heatlosses of the stator.

It is, of course, desirable to maintain turbo-generators in particularthose of large dimensionsat constant temperature, independently of theload thereon, in order to avoid as much as possible relative shiftingbetween copper conductor and iron due to the different expansions ofboth substances. Here it also is necessary to adapt the velocity of flowof the cooling gas in the rotor to the respective current load of therotor. This possibility is not offered by the above-mentioned knowninstallations; however, it can be achieved in a simple way in my novelinstallation of a special cooling gas circulating apparatus disposedoutside of the generator, whereof the gas flow actuated thereby is maderegulatable.

In the following the invention will be explained in detail by way of anillustrative example, and with reference to the appended drawing,wherein:

Fig. 1 diagrammatically represents a practical embodiment of aturbo-generator-cooling system, illustrative of principles of theinvention; and

Fig. 2 diagrammatically represents another embodiment of the invention.

In the drawing, a stator of a turbo-generator is designated at 1, whilethe rotor of said generator is indicated at 2. For the cooling of thestator, fans 3, 3, are pro- 'ice vided at both ends of the rotor shaft,which fans produce in known way currents of cooling gas flowing throughthe air gap 4 of the engine and through radial slots in the stator, andfinally through the space between stator and casing 5; said gas currentsare cooled in coolers 6 adjacent the ends of stator 1. For the actuationof the gas flow cooling principally the rotor, there is provided acooling gas circulating apparatus 7 which may, in particular, include acompressor of arbitrary construction, driven by a motor 8, or, undercertain circumstances, also by direct or indirect coupling with thegenerator shaft. Gas is drawn off from the apparatus by a pipe line 9through one or more apertures 10 in the casing 5, preferablyapproximately in the center of the latter, and is forced through thecooler 11 after an increase in pressure in the gas circulating apparatus7, effecting the required velocity of cooling gas flow. Said gas arrivesfrom the gas circulating-cooling assembly through the pipe lines 12, 13into annular spaces 14, 14 around the shaft, disposed at both ends ofthe rotor shaft, wherefrom it flows through axial ducts 14a, 14a in therotor 2 to the apertures of these ducts communicatiug with the air gap 4to reach the suction apertures 10 through radial cooling slots in thestator.

The annular spaces 14, 14 are sealed against the remaining internalspace of the turbo-generator by labyrinth packings 15, 15 so that thecooling gas current provided for the cooling of the rotor can be mixedwith the remaining gas, present in the internal space only when the samehas passed through the rotor.

In order to be able to modify the velocity at which this cooling gascurrent passes through the rotor, indepeudently of the velocity of thegas circulation, an adjustable choking device 16 is provided in the pipeline 12. Instead of changing the velocity of flow of this gas stream bya choking device, the same result can also be effected by a modificationof the speed of the cooling gas circulating apparatus or of the enginedriving the latter. It is possible to apply both means simultaneously. Y

If the cooling gas, preferably hydrogen, in the generator is subjectedto a comparatively high pressure, for example 3 atm., the gascirculating apparatus needs to produce only a comparatively smallincrease in pressure, for example an increase in pressure from 3 to 3.1atm., in order to provide the required velocity of flow in the rotor.

In order to apply the shaft packings of the cooling gas circulatingapparatus only for this difference in pressure it is possible, accordingto a further construction of the invention, to enclose the cooling gascirculating apparatus together with its driving means in a gas-tightcasing 17 wherein preferably almost the same pressure prevails as in thegenerator casing, so that leakage losses of the compressor or its shaftpackings can practically be eliminated. To avoid leakage losses in thecooler, this latter can also be, and preferably is, enclosed in thegas-tight casing 17.

According to an additional construction of the invention, the suctionside and the pressure side of the gas circulating apparatus can becombined by way of a bypass line 18 provided with a latchable dampermeans 19 which is locked in the normal operation and opens automaticallywhen the feed pressure ceases, e.g., when the cooling gas circulatingapparatus is out of operation. In this way a certain flow is stillmaintained, if the gas circulating apparatus is out of service, by meansof the inherent pressure of the rotor through the open damper means 19and the rotor ducts.

Independently thereof, an additional connection between the suction sideand the pressure side of the gas circulating apparatus can be providedby means of a high-pressure relief valve to prevent undesirably highvalues of the pressure on the pressure side of the gas circulatingapparatus when the gas flow is choked by the throttle device 16.

- The actuation of the throttle device 16 and/ or :of the shiftingdevice for the speed of the cooling gas circulating apparatus can .beregulated-according to a further development of the invention-byappropriate regulating devices of known type in inter-relation to amagnitude effected by the load of the generator. The load current or theexciting current of the generator or the temperature of the rotor can,for example, be used as such a magnitude.

The invention is not limited to the specific embodiment depicted. Thereare, e.g., feasible modifications in the sequence of gas circulator7-cooler 11and throttle device 16. Under some circumstances, it may beexpedient to dispose the cooler for the rotor losses on or in thegenerator,

In the constructional example described above and illustrated in thedrawing an arrangement is shown wherein thecooling system for the rotoris not completely separate from the cooling system for the stator inthat the two systems join in the middle of the machine. It is to beunderstood, however, that the present invention is not restricted tosuch intermingling of the two cooling gas streams but rather that theinvention includes the embodiment according to which both coolingsystems are completely separate. In the case of completely separatecooling systems for the rotor and stator, the stator system is separatedfrom the rotor system and the cooling gas for the rotor enters at oneend of the rotor and passes through the axial rotor ducts to the otherend of the rotor, without there being any communication in the centre ofthe machine between the rotor and stator cooling systems. An example ofsuch separate cooling systems is shown in Fig. 2 where the same elementsas in Fig. 1 are designated by the same numbers.

.I claim:

1. In a turbo-generator having a casing, a stator within and spaced fromsaid casing, and a rotor rotatably mounted within said stator by a rotorshaft; a common gas cooling system for cooling said rotor and statorcomprising a cooling gas circulating apparatus positioned outside saidturbo-generator casing, said circulating apparatus having a pressureoutlet and a suction inlet, said stator having a plurality of radialcooling slots therein longitudinally spaced along the length thereof,said rotor having at each end cooling ducts extending axially throughthe rotor toward the center thereof and opening radially outwardly atthe central portion of said rotor, said casing having annular chambersat each end of the rotor in communication with therotor axial ducts,first conduit means connecting the pressure outlet of said cooling gascirculating apparatus with said annular chambers and second conduitmeans connecting the suction inlet of said circulating apparatus with anopening in the central portion of said casing opposite the centralradial openings in said rotor whereby cooling gas is circulated fromsaid circulating apparatus outlet to the annular chambers, through theaxial cooling ducts in said rotor and radially outwardly from thecentral portion thereof through at least some of the stator radialcooling slots for return to said gas circulating apparatus through saidsecond conduit means, and fan means mounted at each end of the rotorshaft within said casing for circulating a portion of the cooling gasfrom the central portion of the space intermediate the stator and thecasing adjacent the casing outlet in separate streams toward the .endsofthe stator, through the air gap between the rotor and the stator, andradially outwardly through the radial cooling slots in the stator.

2. Apparatus as defined in claim 1 and further including means forregulating the cooling gas flow produced by said cooling gas circulatingapparatus.

3. Apparatus as defined in claim 2 wherein saidcooling gas is enclosedin a gas-tight casing and includes a gas cooling device and a drivingmotor.

4. Apparatus as defined in claim 1 and further .including auxiliarycooling means in said turbo-generator casing for cooling the portion ofthe gas recirculated by the fan means.

5. Apparatus as defined in claim 1 wherein the ends of the rotor shaftare journalled in the casing annular chambers and further includinglabyrinth packing means cooperating with the rotor shaft ends forsealing the spaces Within the annular chambers from the interior of theturbo-generator casing.

References Cited in the file of this patent UNITED STATES PATENTS1,030,556 Williamson June 25, 1912 1,522,333 Schroeder lan..6, 19251,816,489 Kuyser July 28, 1931 2,451,219 Holmgren Oct. 12, 19482,663,808 Rosenberg Dec. 22, 1953 2,707,244 Kilgore Apr. 26,1955

FOREIGN PATENTS 896,086 Germany Nov. 9, 1953

